In recent years, electrophotography technology has been widely used and applied not only in the area of copying machines but also in the area of various printers and printing machines especially because it can produce high-quality images with immediacy.
The core of the electrophotography technology are electrophotographic photoreceptors, whose conventionally used photoconductive materials are inorganic photoconductors such as selenium, arsenic-selenium alloy, cadmium sulfide, and zinc oxide; the recent mainstream is the electrophotographic photoreceptors using organic photoconductive materials, which have the advantages of entailing no pollution, ensuring easy film-forming, being readily manufacturable, etc.
The sensitivities of the electrophotographic photoreceptors using organic photoconductive materials vary depending on the kinds of their charge generation materials. As charge generation materials that have sensitivity to long wavelengths of, for example, 600 nm-800 nm, phthalocyanine compounds have been attracting attention and studied energetically. Especially eager study has been conducted on metal-containing phthalocyanines such as chloroaluminium phthalocyanine, chloroindium phthalocyanine, oxyvanadyl phthalocyanine, hydroxygallium phthalocyanine, chlorogallium phthalocyanine, magnesium phthalocyanine, oxytitanyl phthalocyanine, etc., as well as metal-free phthalocyanines and the likes.
Non-Patent Document 1 discloses that even if the structure of the individual molecule is identical, a phthalocyanine compound may exhibit various charge generation efficiencies in the state of crystal, which is the aggregation of molecules, according to the regularity in arrangement of molecules (crystal form).
Patent Documents 1-4 disclose studies on a crystalline phthalocyanine compound that contains effective components having a single structure. In addition, studies have been conducted also on a composite that contains a nonsubstituted phthalocyanine and a substituted phthalocyanine as effective components (see, e.g., Patent Documents 5-7) and a composite that contains nonsubstituted phthalocyanines having different central metals in combination (see, e.g., Patent Documents 8-11).
As regards the photosensitive layers of the electrophotographic photoreceptors, inorganic photoconductive substances such as selenium, cadmium sulfide, zinc oxide, amorphous silicon, etc. have been widely used. In recent years, various organic photoconductive substances have been examined for their application to the electrophotographic photoreceptor's photosensitive layers, some of which substances have already been put to practical use. Compared with inorganic compounds, the organic photoconductive substances have the advantages of being lightweight, ensuring easy film-forming, facilitating photoreceptor manufacturing, enabling transparent photoreceptors according to their kinds, containing no pollution-causing materials, etc.
As structures of the photosensitive layers, there are known the single-layer type photosensitive layer, in which a charge generation substance and a charge transport substance are contained in the same layer and dispersed in binder resin, and the so-called functionally-separated type photosensitive layer, in which the function of generating charge carriers and the function of transporting charge carriers are separately served by different compounds. Above all, the multilayer type photosensitive layer having a charge generation layer, which contains a charge generation substance dispersed in binder resin, and a charge transport layer, which contains a charge transport substance dispersed in binder resin, has become the mainstream of development because of its effectiveness in improving the sensitivity, and organic photoreceptors of this type have been put to practical use.
Organic photoconductive substances known to serve as charge generation substances are: phthalocyanine materials such as metal-free phthalocyanines and metal-containing phthalocyanines; various kinds of organic pigments such as perynone pigments, indigos, thioindigos, quinacridones, perylene pigments, anthraquinone pigments, azo pigments, bisazo pigments, trisazo pigments, tetrakisazo pigments, cyanine pigments, polycyclic quinones, pyrylium salts, thiopyrylium salts, anthanthrones, and pyranthrones; and dyes.
Phthalocyanine materials, in particular, show high sensitivity in the long wavelength region and are known in variety of kinds, among which the titanyl phthalocyanine compounds having particular crystal forms are known to show especially excellent sensitivity (e.g., Patent Document 12).
[Patent Document 1] Japanese Patent Laid-Open Publication No. Sho 62-67094
[Patent Document 2] Japanese Patent Laid-Open Publication No. Hei 5-98181
[Patent Document 3] Japanese Patent Laid-Open Publication No. Hei 5-263007
[Patent Document 4] Japanese Patent Laid-Open Publication No. Hei 10-67946
[Patent Document 5] Japanese Patent Laid-Open Publication No. Hei 9-120171
[Patent Document 6] Japanese Patent Laid-Open Publication No. 2002-251026
[Patent Document 7] Japanese Patent Laid-Open Publication No. Hei 10-48859
[Patent Document 8] Japanese Patent Laid-Open Publication No. 2000-336283
[Patent Document 9] Japanese Patent Laid-Open Publication No. Hei 4-372663
[Patent Document 10] Japanese Patent Laid-Open Publication No. Hei 6-175382
[Patent Document 11] Japanese Patent Laid-Open Publication No. Hei 5-45914
[Patent Document 12] Japanese Patent Laid-Open Publication No. Hei 2-008256
[Non-Patent Document 1] Electrophotography: the society journal, 1990, Vol. 29, No. 3, pp. 250-258.